1. Field of the Invention
The present invention relates to an axle driving apparatus, whose output speed is changed by manipulation of a traveling control member, wherein the human operational force to be applied onto the traveling control member can be reduced.
2. Background Art
Conventionally, there is a well-known axle driving apparatus having a construction such that a hydraulic pump driven by an engine, a hydraulic motor fluidly connected with the hydraulic pump and an axle driven by output rotation of the hydraulic motor are incorporated in a common housing. Hereinafter, such an axle driving apparatus is referred to as an integrated hydrostatic transmission, namely, an xe2x80x9cIHTxe2x80x9d. Also, hereinafter, a hydrostatic transmission constituted by the hydraulic pump and the hydraulic motor fluidly connected with each other is referred to as an xe2x80x9cHSTxe2x80x9d.
At least either the hydraulic pump or the hydraulic motor is of a variable displacement type provided with a capacity changing device like a movable swash plate in connection with a human-operated traveling control member. The capacity thereof is continuously varied according to the operational degree of the traveling control member so as to continuously change the rotational speed of the axle.
The IHT is lightened and compacted because the hydraulic pump, the hydraulic motor and the axle are incorporated together in the common housing, thereby being advantageous in compacting a vehicle equipped with the IHT. However, if the vehicle travels with the axles under a heavy load, an operator is troubled to apply a great force onto the traveling control member for the speed changing operation, thereby hindering a smooth speed changing.
An object of the present invention is to provide an IHT which can be smoothly operated in its speed changing by reduced human force.
To attain the object, a hydraulic actuator such as a hydraulic cylinder is provided for controlling the capacity changing device. The hydraulic actuator comprises a driving part and a fixed part. The driving part is operatively connected to the capacity changing device. If the capacity changing device is a rotationally movable swash plate, a connection member is interposed between the driving part of the hydraulic actuator and the movable swash plate so as to alter the reciprocal movement of the driving part to the rotational movement of the movable swash plate.
The fixed part of the hydraulic actuator is fixed to the housing. Moreover, if a center section is fixed to the housing for fluidly connecting the hydraulic pump and the hydraulic motor with each other, the center section may serve as the fixed part of the hydraulic actuator, thereby reducing the number of parts required to produce the hydraulic actuator. Also, in this case, the driving part is incorporated in the center section, thereby contributing for minimization of the IHT. Furthermore, the control valve may be also incorporated in the center section so as to further minimize the IHT. In this case, the control valve may be reciprocally movable in parallel to the driving part of the hydraulic actuator, thereby extremely reducing the waste portion of the center section for arrangement of the hydraulic actuator and the control valve.
The hydraulic actuator is hydraulically controlled by a control valve. For operating the control valve, a link mechanism operatively connected to a human-operated traveling control member provided on a vehicle is supported by the housing so as to be connected to the control valve. All the human operational force to be applied onto the traveling control member may be just as much as that required to move the control valve through the link mechanism. Thus, the human operational force for speed change can be reduced so as to enable the vehicle to be tirelessly driven even for a long time.
Preferably, for minimizing the hydraulic servomechanism comprising the hydraulic actuator, the control valve and the link mechanism, the control valve is reciprocally movable in parallel to the driving part of the hydraulic actuator. The link mechanism comprises a rotary member rotatably supported by the housing and a link member interposed between the rotary member and the control valve. The rotary member is operatively connected to the traveling control member. The link member alters the rotational movement of the rotary member into the reciprocal movement of the control valve.
The driving part of the hydraulic actuator may be connected to the link member for its feedback. For preventing the human force required to operate the control valve from increasing, a portion of the link member between its connection points with the rotary member and the control valve is provided for connection with the driving part of the hydraulic actuator.
The link mechanism, or especially, the rotary member can be provided as an effective portion to which a neutral returning means for returning the capacity changing device to its neutral position is attached. That is, by biasing the link mechanism or the rotary member to its neutral position, the neutral position of the capacity changing device can be defined.
For supplying oil into the,hydraulic actuator through the control valve, the oil filled in the housing may be used. Moreover, when a charge pump for supplying the HST with oil is provided in the housing, the charge pump may also be used for supplying the hydraulic actuator with oil. Oil from the hydraulic actuator may be drained into the inner space of the housing. Therefore, any other oil source is not required for the hydraulic actuator, thereby saving the number of parts for constituting the hydraulic servomechanism for moving the capacity changing device so as to save costs.
The hydraulic actuator and the control valve may be contained in the common housing. Moreover, the link mechanism may be also contained in the housing except for a portion thereof in connection with the human-operated member provided outside the housing. Thus, the oil circuit for supplying the hydraulic cylinder and the control valve with oil from the oil sump in the housing can be extremely minimized so as to enable the IHT with such a hydraulic servomechanism to be excellently compact. Also, such component parts of the hydraulic servomechanism for moving the capacity changing device are protected by the housing from muddy water, rain water, dust and other impurities so as to improve the durability and reliability of the IHT in its capacity control.
The above, further and other objects, features and advantages will appear from the following description.